This invention relates to A microprocessor device with an integrated timer, and more particularly to a microprocessor used in an adapter for coupling a host processor to a data communications loop, in which the microprocessor contains an integrated timer for defining system functions.
The token-ring local area network is a data communications system functioning to transfer data among a number of stations coupled to a one-way signal path. Each station has a host processor with memory and various peripheral devices to function as an independent workstation. Access to the ring is controlled by token passing wherein a free or busy token is passed from one station to the next around the ring. An early example of the token ring is shown in U.S. Pat. No. 3,597,549 issued to Farmer & Newhall and assigned to Bell Telephone Laboratories. In further refinement, the so-called Munich ring has evolved from developments by IBM, reported at Proceedings of the National Telecommunications Conference November 1981, pp. A.2.2.1-A.2.2.6. Standard protocols for these communcations methods have been published by the IEEE as the 802.5 token ring proposal, and a similar report by the European Computer Manufacturers organization.
The present invention is concerned with a microprocessor device used in an adapter for connection between the host processor and the signal path of the ring. This adapter defines a number of timed functions which are part of the protocol for token-ring networks. The adapter must operate relatively independent of the CPU of the host processor so that a minimum of interference with the functions of the host CPU is needed. The adapter must accomodate a variety of different types of host CPU, so that a special adapter need not be manufactured for each different type of construction of the workstations. It is expected that entire office buildings for manufacturing facilities will be permanently wired to implement loop communications of this type between all computer terminals, word processors, telephones, bulk data storage stations, and the like. Thus, the adapters must be of relatively low cost, must be reliable and require little maintenance, must be of small size and dissipate little power, and above all must interface with a variety of differing systems.
It is the principal object of this invention to provide an improved microprocessor device for use in a data communcations system or the like, particularly a microprocessor for use in a communications adapter for coupling a host processor system to a token-passing communications loop. Another object is to provide a microprocessor with integrated timer for use in a communications adapter which has processing and control facility independent of the host system, and which operates with a variety of different host systems. A further object is to provide a microprocessor device for a low cost, low power, reliable and versitile communications adapter for token ring local area network systems or the like.